Flexible drill string joint

ABSTRACT

Upper and lower subs are short coupled by a ball and socket connection embodying a torque-absorbing spline means loose enough not to interfere with flexing of the two subs about the center of their connection.

United States Patent [191 Sutliff et al. [451 May 22, 1973 [54] FLEXIBLE DRILL STRING JOINT [56] References Cited [76] Inventors: Wayne N. Sutliif; Jim L. Downen, UNITED STATES PATENTS both of 2931 Pierce Rd Baker- 2,779,570 1/1957 Roper ..64/7 fi ld C lif 93303 2,893,222 7/1959 Albedyhl et al..... ..64/7 3,142,972 8/1964 Spaulding ..64/7

Filed: July 19, 1971 Appl. No.: 163,898

Primary Examiner-Charles J. Myhre Assistant Examiner-Randall Heald Attorney-Dana E. Keech [57] ABSTRACT Upper and lower subs are short coupled by a ball and socket connection embodying a torque-absorbing spline means loose enough not to interfere with flexing of the two subs about the center of their connection.

4 Claims, 3 Drawing Figures FLEXIBLE DRILL STRING JOINT SUMMARY OF THE INVENTION It is customary to run drill collars on the lower end of the drill pipe, while drilling, to increase the kinetic energy locally applicable to a fish through a hydraulic jar assembled in the middle of the drill collar section of the string, in case a fishing job becomes necessary. These drill collar sections are often several hundred feet in length and are quite heavy and rigid. In slant or directional drilling operations, the jar in this assembly is subjected to severe bending strains, often resulting in the jar parting.

It is an object of the present invention to provide a means by which jars employed under these circumstances may be protected from excessive bending strains and the useful life of a jar thus extended.

Another object is to provide a relatively inexpensive flexible drill string joint, two of which, when inserted in the drill string, one just above and the other just below a hydraulic jar assembled with said string, will protect the jar from bending strains commonly suffered by such ars.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a small-scale fragmentary view of a section of a drill string including two drill collars, two flexible joints of the present invention, and a hydraulic jar assembled consecutively, with the flexible joints spacing the jar from the drill collars and with the assembly as a whole, bent, as often occurs in deep well drilling operations, to illustrate the protection afforded the jar by the presence of the two flexible joint units in the assembly.

FIG. 2 is an enlarged-scale longitudinal sectional view taken on line 2-2 of FIG. 1 of the preferred embodiment of the flexible drill string joint of the inventron.

FIG. 3 is an enlarged cross-sectional view taken on line 33 of FIG. 2, and illustrates the loose fit between the male and female spline subs of the invention which affords a substantial degree of flexibility in the joint.

DESCRIPTION OF THE PREFERRED EMBODIMENT A portion ofa drill string shown diagrammatically in FIG. 1 includes a drill collar 11, a drill collar 12, a hydraulic jar 13 and two flexible drill string joints 14, embodying the present invention and which connect the upper and lower ends of the jar 13 respectively with the upper and lower drill collars 11 and 12. The drill collars 11 and 12 are shown in this view inclined slightly to the left from the vertical axis of the jar 13, thus causing a curvature in the drill string 10 which, in practice, has a tendency to subject a jar l3 assembled in the drill string to bending strains which often cause severe damage to the jar. As aforestated, it is the object of the drill string joints 14 to flex readily when subjected to a bending strain so as not to transmit such strains to the jar 13 when opposite ends of the latter are connected to the balance of the drill string through such flexible drill string joints.

Each drill string joint 14 includes an upper sub 15 and a lower sub 16. The upper sub has an internally threaded box 17 which is adapted to be screwed onto the threaded pin 18 provided at the lower end of a drill string element such as the jar 13. Provided axially in the sub 15 is a bore 19 which is relatively short and terminates in a counter bore 20, the lower end portion of which is provided with internal threads 25.

The lower sub 16 terminates at its lower end in an externally threaded pin section 26 which is adapted to screw into an internally threaded box section 27 such as is provided on the upper end of drill collar 12 of drill string 10 shown in FIG. 1. An upper portion of the lower sub 16 is tooled away to leave a male spline section 28 having three male splines 29 radiating therefrom in equally circumferentially spaced relation. Between the spline section 28 and the upper end of the lower sub 16, the latter is provided with external threads 30. At the lower end of the male spline section 28, the lower sub 16, where this is milled away, is left with a concave spherical face 31 which is generated about a center point 32. Loosely slideable axially onto the male spline section 28 is a female spline section 33 having three internal splines 34 which loosely interfit with the male splines 29. The upper end portion 35 of section 33 is externally threaded so as to readily screw into the internal threads 25 of the upper spline section 15. The lower end of female spline section 33 is provided with a convex spherical face 40 which slideably fits the concave spherical face 31 on the lower sub 16.

Captured in the counter bore 20 by the female spline section 33 when this is screwed into the threads 25 of the upper sub 15, are upper and lower ball socket rings 41 and 42 and a ball 43 which is internally bored and threaded to screw onto the threads 30 provided on the upper end of lower sub 16 so that the center of said ball is located at point 32. The socket rings 41 and 42 are shaped spherically to conform to and provide a bearing socket for said ball. The upper extremity of lower sub 16 is spherically formed about center point 32 with the same radius as the ball 43. Suitable O-rings 44 and 45 are provided in socket rings 41 and 42 for sealing off the space 46 within the counter bore 20 opposite the ball 43 to prevent contamination of lubricant injected into this space through an aperture 47 formed in the upper sub 15 and normally closed by a plug 48.

The ball 43 is thus well lubricated at all times and free to rotate about the center 32 relative to the upper sub 15 to the extent allowed by the looseness of the fit between the male spline section 28 of the lower sub 16 and the female spline section, 33 of the upper sub 15. Only a relatively small angle of flexibility between the two subs is requisite for the invention to give the necessary protection to the hydraulic jar 13 in the drill string 10, and such a flexing of the lower sub 16 relative to the upper sub 15 is indicated by broken lines 50 in FIG. 2.

OPERATION The lower sub 16 is provided with a central circulating fluid passage 51 which connects through a passage 52 in the upper socket ring 41 with the bore 19 of upper sub 15. Provision is thus made for the free passage of circulating liquid through the joint 14. A loose fit is provided between the spherical surfaces 31 and 40 through which ambient circulating liquid may be readily admitted to the space between the spline sections 28 and 33 for lubrication of the surfaces thereof.

Axial forces of thrust and tension are transmitted through the joint 14 by the ball and socket connection provided between the upper and lower subs l5.and 16, while torque forces are transmitted through this joint between these subs by the interaction of the male and female spline sections 28 and 33.

Four spring wells 55 are provided in the upper end of upper socket ring 41 to confine coiled springs 56 for spring biasing the ring 41 against the ball 43 and take up any play which might develop between the ball and ring 42.

We claim:

1. in a flexible drill string joint the combination of:

an upper sub;

a lower sub;

pin and box means on said subs for connecting the same respectively to juxtaposed sections of a drill string so as to assemble said joint in said string;

said upper sub having a central bore for conducting circulating liquid therethrough and a counterbore internally threaded at its lower end;

a female tubular spline section externally threaded at its upper end to screw into said counterbore threads and form a shoulder extending into said counterbore, said female spline section having female splines extending radially inwardly therefrom;

an upper portion of said lower sub being tooled away to leave a male spline section having male splines radiating therefrom in equally circumferentially spaced relation to inter-engage with said female splines for transmitting torque from said upper sub to said lower sub;

a ball mounted on the upper end of said male spline section and occupying a smooth portion of said counterbore; and

upper and lower ball socket rings occupying upper and lower positions in said smooth portion of said counterbore, said rings conforming to and providing a bearing socket for said ball and forming a liquid tight seal between said upper and lower subs;

there being circulating fluid passageways formed axially in said lower sub and in said upper ball socket ring which connect with each other and with the circulating liquid passageway provided in said upper sub.

2. A combination as recited in claim 1 wherein spring means are provided for axially biasing said upper ball socket ring downwardly against said ball to maintain a constant fluid tight fit between said ball, said ring and said counterbore so as to prevent escape of circulating liquid flowing through said passageways.

3. A combination as recited in claim 2 wherein O-ring means are provided to provide fluid tight seals between said upper and lower ball socket rings, said ball, and said counterbore.

4. A combination as recited in claim 1 wherein each of said spline sections has three radially extending spline teeth equally spaced circumferentially from each other, the spline teeth of each of said sections loosely interfitting with the spline teeth of the other section, said spline sections thereby permitting the flexing of said lower sub relative to said upper sub through a substantial angle in any direction, relative to the center of said ball, while said joint and the drill string embodying the same are rotating. 

1. In a flexible drill string joint the combination of: an upper sub; a lower sub; pin and box means on said subs for connecting the same respectively to juxtaposed sections of a drill string so as to assemble said joint in said string; Said upper sub having a central bore for conducting circulating liquid therethrough and a counterbore internally threaded at its lower end; a female tubular spline section externally threaded at its upper end to screw into said counterbore threads and form a shoulder extending into said counterbore, said female spline section having female splines extending radially inwardly therefrom; an upper portion of said lower sub being tooled away to leave a male spline section having male splines radiating therefrom in equally circumferentially spaced relation to inter-engage with said female splines for transmitting torque from said upper sub to said lower sub; a ball mounted on the upper end of said male spline section and occupying a smooth portion of said counterbore; and upper and lower ball socket rings occupying upper and lower positions in said smooth portion of said counterbore, said rings conforming to and providing a bearing socket for said ball and forming a liquid tight seal between said upper and lower subs; there being circulating fluid passageways formed axially in said lower sub and in said upper ball socket ring which connect with each other and with the circulating liquid passageway provided in said upper sub.
 2. A combination as recited in claim 1 wherein spring means are provided for axially biasing said upper ball socket ring downwardly against said ball to maintain a constant fluid tight fit between said ball, said ring and said counterbore so as to prevent escape of circulating liquid flowing through said passageways.
 3. A combination as recited in claim 2 wherein O-ring means are provided to provide fluid tight seals between said upper and lower ball socket rings, said ball, and said counterbore.
 4. A combination as recited in claim 1 wherein each of said spline sections has three radially extending spline teeth equally spaced circumferentially from each other, the spline teeth of each of said sections loosely interfitting with the spline teeth of the other section, said spline sections thereby permitting the flexing of said lower sub relative to said upper sub through a substantial angle in any direction, relative to the center of said ball, while said joint and the drill string embodying the same are rotating. 